the field artillery journal - Fort Sill - U.S. Army

Back Toward
Fundamentals
By Maj. A. R. Hercz, FA
With the present trend of artillery survey away
from plane tabling and inclining more and more to
transit work, it might be appropriate to cast back a glance
at "the good old fashioned way" with an eye to salvaging
what is worth while. The principle advantages of the allbut-forgotten
plane-table are: that no computations are
necessary in order to get final results, or else that no notes
need be kept for interpretation and replot later; and that a
solution to the survey is developed graphically, on the
ground, where it may be compared with the terrain at each
point of progress. Therefore less training is necessary and
fewer mistakes will result than by use of computed survey.
Also many problems (such as resections) may be worked
out graphically with comparative ease, while the same
problems solved analytically using transit data are quite
complicated.
While the transit is, of course, more accurate, a plane-
Figure 1
204
Figure 2
table survey to an appropriate scale has all the accuracy
required for artillery purposes (with the sole exception of
short-base triangulation).
The chief objections to planetabling are not due so much
to the methods as to the poor equipment generally used.
Anyone who has stood in the wind on Bald Ridge trying to
find the Water Tank in Elgin through his open sight while
the wind whipped out a tune on the front sight hair, or who
tried to unscramble the magnetic bearing while his needle
bounced from one side of the declinator box to the other,
knows what is meant.
However, with the device described below it is believed that
the plane table will still be found very useful for many artillery
surveys, such as the position area survey of a battalion.
The only new item required is shown in Figs. 1 and 2. It
simply consists of a brass straight edge near
one end of which a post is rigidly mounted, and
near the other end of which there is a small
knob for a handle. This can be made in any
machine shop from the dimensions given in
Fig. 3, which also indicates the only critical
machining. A scale along the plotting edge is
handy but not necessary.
USE
To use this instrument mount an aiming
circle on the post in the same way that it fits
onto its regular tripod (Fig. 2). In using this
alidade the principles are the same as for any
other type, except for the added upper and
lower motions and compass needle. These
allow several short cuts in operation:
A. To set up and orient on a known
visible point: